1. Field of the Invention
The present invention relates to an inlet valve, as well as an internal combustion engine and a transportation apparatus each including the inlet valve. In particular, the present invention relates to a technique that increases intake air volume.
2. Description of the Related Art
A conventional inlet valve is of a poppet type, and basically includes a valve stem and a valve head (as disclosed in Japanese Unexamined Patent Publications Nos. H05-39706 and 2008-88959, and the like).
The technique of Japanese Unexamined Patent Publication No. H05-39706 is intended to improve, in an inlet device that causes fuel to contact a valve head of an inlet valve so as to combust the fuel, combustion in a combustion chamber by making the fuel concentration distribution uniform. There is disclosed in Japanese Unexamined Patent Publication No. H05-39706, an inlet valve including a valve head provided on a rear surface with a plurality of grooves in substantially concentric circular shapes. A fuel injection valve provided in an inlet pipe sprays a fuel toward the rear surface of the valve head of the inlet valve. Air mixed with the fuel is guided along the plurality of grooves so as to spread into an entire circumferential area on the rear surface of the valve head, and is then taken into a combustion chamber. Since the fuel is uniformly dispersed (that is, no portion of high or low fuel distribution occurs) as described above, it is possible to improve combustion.
The technique of Japanese Unexamined Patent Publication No. 2008-88959 is intended to improve a packing efficiency of an internal combustion engine in the intake stroke by causing air (inclusive of an air-fuel mixture as well as air alone mixed with no fuel) to smoothly flow from an inlet port into a combustion chamber. There is disclosed in Japanese Unexamined Patent Publication No. 2008-88959, an inlet valve provided with a stepped part (barrier) between a valve surface and an inclined surface that is formed in a substantially conical shape from a tip to a circumferential edge portion of a valve head so as to be stepped downward from the valve surface. This inlet valve causes intake air flowing along the inclined surface of the inlet valve to hit the stepped portion so as to form eddies around the stepped portion. Thus, intake air flows smoothly on the surface of the valve head. As a result, air can be smoothly taken into a combustion chamber from an inlet port.
The inlet valve described in Japanese Unexamined Patent Publication No. H05-39706 is not intended to increase an intake air volume. On the other hand, the inlet valve described in Japanese Unexamined Patent Publication No. 2008-88959 is intended to increase an intake air volume. However, more dynamic power will be generated with an intake air volume that is further increased relative to the intake air volume of the inlet valve described in Japanese Unexamined Patent Publication No. 2008-88959.